Micromonochromator and method for producing same

ABSTRACT

A micromonochromator is formed on a substrate and includes a diffraction device ( 6 ) associated with an entry that includes at least one entry point and an exit that includes at least one exit point. A mobile arrangement of light guidance ( 2 - 20, 4 - 26 ) is associated with the entry or the exit or both, and a recovery device ( 23 ) is provided by the exit. The mobile arrangement includes at least one mobile beam integrated in the substrate and equipped with at least one light guide. The mobile beam is able to sweep the entry and/or exit in a continuous manner.

FIELD OF THE INVENTION

This invention concerns a micromonochromator and a process for makingit.

It is applied in particular to:

wavelength multiplexing and demultiplexing in the field of opticaltelecommunications, and

spectrometry.

STATE OF THE ART

It is known that a micromonochromator includes means of diffractionassociated with at least one entry point and at least one exit point.

These means of diffraction may be made with a diffraction mirror or amicroguide network (phase-array) for example.

For spectrometry applications, a micromonochromator is used to measurevariations in intensity on several wavelengths by sweeping severalwavelengths by the means of diffraction.

To do this, the means of diffraction are turned and/or the exit pointassociated with a continuous photodetector is swept by a slit.

With regard to known micromonochromators including several entry pointsand/or several exit points, the following document can be consulted:

Microspectrometer system based on integrated optic components inpolymers and spectral detection system for the VIS- and NIR range, C.Muller, O. Fromhein, J. Gottert, T. Kuhner, J. Mohr, Proc. 7th. Eur.Conf. on Int. Opt. (ECIO '95), Th A2, Applications of Integrated Optics,p. 491 to 494.

In the case of multiplexing/demultiplexing or spectrometry, these pointsare positioned from the outset in a fixed manner, which, particularly inthe case of spectrometry, does not allow for continuous measurement.

SUMMARY OF THE INVENTION

The purpose of this invention is to correct these drawbacks.

The micromonochromator, the subject of this invention, allows forcontinuous sweeping of the wavelength and not just discrete spectralmeasurement as was the case with the prior art.

This allows for improved spectral resolution of microspectrometers.

In the area of multiplexing, the micromonochromator of this inventionhas the advantage of allowing for adjustment of the central wavelengthof a multiplexer after manufacturing of this micromonochromator.

In addition, during multiplexing this micromonochromator allows for freecommutation on the desired transmission channel.

The micromonochromator of this invention is preferably made by anyintegrated optic technique (in particular for making continuouswavelength micromonochromators and mobile microguides).

Such a technique allows for collective manufacturing ofmicromonochromator components.

The invention applies to both multimode and monomode guide structures.

Precisely, this invention concerns a micromonochromator formed on asubstrate and including means of diffraction associated with an entryincluding at least one entry point and an exit including at least oneexit point, this micromonochromator being characterised in that it alsoincludes:

mobile means for light guidance associated with this entry or this exitor both, the mobile means of light guidance including at least onemobile beam integrated in the substrate and equipped with at least onelight guide, this mobile beam being apt to sweep the entry and/or theexit in a continuous manner, and

means for recovery to recover the light supplied by this exit.

In the case of multiplexing/demultiplexing, these means of guidanceallow for optimisation of the positioning of the various entry/exitpoints and, in the case of spectrometry, they allow for continuousmeasurement.

According to a particular mode of manufacturing, the mobile beam isassociated with the entry and equipped with a source of light installeddirectly on this beam.

The means of recovery could include photodetection means to detect thelight supplied by the exit or the means of light guidance (which couldbe fibre optics).

The mobile means of light guidance could include a first mobile means oflight guidance associated with the entry of the micromonochromator, anda second mobile means of light guidance associated with themicromonochromator exit, the first and second mobile means of lightguidance including respectively at least a first mobile beam integratedin the substrate and equipped with at least a first light guide, thisfirst mobile beam being apt to sweep the entry in a continuous manner,and at least a second mobile beam integrated in the substrate andequipped with at least a second light guide, this second mobile beambeing apt to sweep the exit in a continuous manner.

This allows for making a multiplexer/demultiplexer apt to recover ortransmit information in series or to make a spectrometer having a largerrange of measurement than the known spectrometers mentioned above.

According to a first particular mode, the first and second beams areindependent of each other. According to a second particular mode, thefirst and second beams are rigidly attached to each other.

According to a particular mode for making the micromonochromator of theinvention, it includes several mobile beams associated with the entryand/or the exit, these beams being independent of each other at theentry and the exit respectively.

According to another particular mode, the micromonochromator includesseveral mobile beams associated with the entry and/or the exit, thesebeams being rigidly attached to each other at the entry and exitrespectively.

If the means of recovery include means for photodetection intended todetect the light supplied by the exit, these means of photodetection caninclude means for transferring light and a photodetector arranged facingone end of the means of transfer or simply at least one photodetector.

This photodetector may be placed directly on the mobile beam, which isthen associated with the exit.

The means of transfer mentioned above include for example at least alight guide or a fibre optic or a lens.

According to a first particular mode for making the micromonochromatorof the invention, the means of diffraction include a mirror withmultiple facets also called a “step grading”.

The positions of the facets can be calculated by the method described inthe following document:

(1) French patent application No. 86 18434 of Dec. 31, 1986corresponding to EP 0 275 795 A and to U.S. Pat. No. 4,786,133 A.

According to a second particular mode, the means of diffraction includea network of light microguides also called “PHASAR”.

The following document may be consulted on this subject:

(2) PHASAR-based WDM-devices: principles, design and applications, MeintK. Smit and Cor van Dam, IEEE Journal of selected topics in quantumelectronics, vol. 2, no. 2, June 1996, p. 236 to 250.

The present invention also concerns a process for manufacturing themicromonochromator of the invention, characterised in that the means ofdiffraction and the mobile means of light guidance are manufactured byan integrated optic technique.

Advantageously, they are manufactured collectively by this integratedoptic technique.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood with a reading of thedescription of the embodiment examples given below, which are purelyindicative and in no way limiting, with reference to the drawings inappendix, in which:

FIG. 1 is a schematic perspective view of a classic micromonochromatormade by an integrated optic technique,

FIG. 2 is a schematic perspective view of a micromonochromator accordingto the invention, including a mobile beam supporting an entrymicroguide,

FIG. 3 is a schematic perspective view of a micromonochromator accordingto the invention, including a mobile beam at its entry and a mobile beamat its exit, these beams each supporting a microguide,

FIG. 4 is a schematic perspective view of a micromonochromator accordingto the invention, including a mobile beam at its entry and a mobile beamat its exit, these mobile beams each supporting a microguide and beinglinked to each other,

FIG. 5 is a schematic perspective view of a micromonochromator accordingto the invention, arranged in the same way as that in FIG. 4 butincluding in addition an electrostatic control comb for the mobilebeams,

FIG. 6 is an overhead schematic view of another micromonochromatoraccording to the invention, including a mobile beam at its entry andmeans of diffraction composed of a microguide network, and

FIG. 7 illustrates schematically a micromonochromator according to theinvention including several mobile beams at the entry for example.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS OF THE INVENTION

It should first be specified that the micromonochromators according tothe invention which are schematically represented in FIGS. 2 to 6 aremade by an integrated optic technique allowing for collectivemanufacturing of all of the components of each micromonochromator andthat the optic adjustment of each of them (positing of the beam or beamswhich it includes) is done by the manufacturing process itself.

For manufacturing of the means of diffraction in the case of FIGS. 2 to5 where these means of diffraction are composed of a multiple-facetmirror, the aforementioned document (1) can be consulted.

For manufacturing of the means of diffraction represented on FIG. 6where these means are composed of a microguide network, document (2) canbe consulted.

With regard to manufacturing of each of the mobile beams equipped with alight guide, the following document can be referred to:

(3) TR 2 660 444 A corresponding to EP 0 451 018 A and to U.S. Pat. No.5,078,514 A.

In an embodiment mode which is not shown, the mobile beams can beequipped with small mechanical radius rods.

The following document may be consulted for this subject:

(4) French patent application No. 94 13559 of Nov. 10, 1994 (FR 2 726905 A) corresponding to EP 0 712 004 A.

When a micromonochromator according to the invention includes a beam atits entry and a beam at its exit, these two beams can be movedsimultaneously if there is a linking rod between the two beams as shownin FIG. 4, or they can be moved independently of each other as is thecase in FIG. 3.

The case of a wavelength multiplexer/demultiplexer will now beconsidered.

For wavelength demultiplexing, the positioning of a mobile beam with theentry guide for the means of diffraction, according to the invention,makes it possible to compensate, after manufacturing, for any drift inwavelength of the demultiplexer (variation in absolute index targetedfor example).

The position of the exit wavelengths of the demultiplexer depends on theshape of the optic component used for the diffraction but also dependson the absolute optic index of the layers made.

The distance between the exit wavelengths varies little as a function ofthe index of refraction of the optic layer.

The position of the exit wavelengths is however very sensitive tovariation of this refraction index.

This variation can be compensated by a modification of the position ofthe entry guide of the means of diffraction.

The calculations in document (1) mentioned above may be consulted onthis subject.

A modification of the position of the entry guide modifies the positionof the exit wavelengths.

This explains the importance of the entry mobile beam.

In addition, making a mobile beam facing the entry to the means ofdiffraction requires leaving a space free between this mobile beam andthis entry.

This free space can be used to introduce any appropriate optic toimprove the performance of the wavelength demultiplexer.

Microlenses or phase shifting plates or anti-reflection layers or anindex liquid may be inserted in this free space for example.

The preceding reasoning is the same in the case of a multiplexer.

In this case, the mobile beam is located at the exit from the means ofdiffraction.

The case of a spectrometer will now be considered.

According to the invention, the card of photodetectors used fordetection in the known spectrometer (see the document Microspectrometersystem based on integrated optic components in polymers as spectraldetection system for the VIS- and NIR Range already cited) is replacedwith a mobile beam with an optic guide and a photodetector at the end ofthe optic guide or a photodetector positioned directly on this mobilebeam.

This allows for continuous detection of the spectrum to be measured, theresolution no longer limited by the dimensions of the photodetectorsused in the prior art.

As was seen above, movement of the entry guide (or exit guide) of themeans of diffraction of a micromonochromator according to the inventionallows for movement of the exit (or entry) wavelengths of thedemultiplexer (or multiplexer) using this micromonochromator.

In the case of the spectrometer, the whole spectrum is shifted.

In some cases this can improve the measurement range of thespectrometer, particularly if the entry and exit beams are associatedwith means of diffraction and are linked to each other.

In this case, when the entry and exit channels of the micromonochromatorare close to each other on the same side of this micromonochromator, asingle control device for the entry and exit beams can be made as isshown schematically in FIG. 5.

FIG. 1 is a schematic perspective view of a known micromonochromatormade with an integrated optic technique.

This micromonochromator in FIG. 1 includes a entry optic microguide 2and several exit optic microguides 4.

It also includes means of diffraction 6 composed of a step gradingplaced facing the entry and exit microguides as can be seen in FIG. 1and which functions by reflection.

These microguides 2 and 4 and the diffraction 6 are formed for exampleon a substrate 8 at the area where there is a set 10 of three layers(two layers of SiO₂ and an intermediate layer of SiO₂ modified so thatit has a refractive index greater than that of the other two layers).

The microguides 2 an d 4 are formed by etching of this intermediatelayer (see document (1)).

In the example shown, a demultiplexer with wavelengths λ1, λ2, λ3 and λ4is sought, for example.

The light with these wavelengths is sent into the microguide 2 anddemultiplexed by the network 6 provided for this purpose.

Four exit microguides 4 are used to recover respectively wavelengths λ1,λ2, λ3 and λ4.

In FIG. 1, reference 14 shows the limits of the optic beam going towardthe diffraction mirror and reference 16 shows the limits of the returnbeam.

A free space 18 has been etched through the set of layers 10 to form thenetwork 6 (see also document (1)).

The micromonochromator according to the invention which is schematicallyrepresented in perspective in FIG. 2 is identical to themicromonochromator of FIG. 1 except that the terminal part of themicroguide 2, which is located facing the network 6, is formed on amobile beam 20 apt to move in a free space 22 formed across the set oflayers 10.

FIG. 2 also shows the means for photodetection 23.

These means for photodetection are to detect the light supplied by eachof the exit microguides 4.

The means of control which are not shown such as for example anelectrostatic control comb are also placed on the substrate 10 in orderto move the mobile beam 20 and thus the extremity of the microguide 2,facing the network 6.

The micromonochromator according to the invention which is schematicallyshown in perspective in FIG. 3 is identical to that of FIG. 2 exceptthat the exit of this micromonochromator has only one microguide 4(instead of four as in FIG. 2).

In FIG. 3, the extremity of this microguide 4 is located on the mobilebeam 26 which is mobile in a free space formed through the set of layers10.

The two beams 20 and 26 are identical and parallel as can be seen inFIG. 3.

The means of control allowing for movement of the mobile beam 26 andthus the corresponding microguide 4 are not shown in FIG. 3.

These means of control can also be an electrostatic control comb.

In the case of FIGS. 1 to 5, the microguides 2 and 4 are located on thesame side of the substrate 8 and, in the case of FIGS. 3 to 5, the beamsare thus also located on the same side of this substrate.

In the case of FIG. 3, the movement of the mobile beam 26 allows forselection of one of the wavelengths demultiplexed by the network 6.

In FIG. 3, the mobile beams 20 and 26 are independent of each other.

In FIG. 4, the mobile beams 20 and 26 are on the contrary rigidlyattached to each other.

More precisely, the micromonochromator according to the invention whichis schematically shown in perspective in FIG. 4 is identical to that ofFIG. 3 except that the beams 20 and 26 are, in the case of FIG. 4,mobile in the same free space 30 formed through the set of layers 10.

In this space 30 there is also a cross bar 32 which is perpendicular tothe beams 20 and 26 and which links them, the extremities of these beamsbeing located facing the network 6.

Thus, any movement of one of the two beams implies movement of the otherbeam.

The means of control for the two beams 20 and 26 are not shown on FIG.4.

FIG. 5 shows an example of such means of control allowing for movementof the two beams 20 and 26.

These means of control are composed of an electrostatic control comb 34activated by means which are not shown.

This comb 34 is formed by an integrated optic technique from the set oflayers 10.

FIGS. 2 and 5 also show photodetectors 23 for detecting the lightsupplied by each exit microguide 4.

In FIG. 2, there are four photodetectors whereas in FIGS. 3 to 5 thereis a single photodetector 23.

In the case of FIGS. 2 to 5, each photodetector is formed facing theextremities of the exit microguides, opposite the extremities facing thenetwork 6.

Instead of this, there can be a photodetector 36 directly formed on themobile beam 4, on the side of one extremity of this mobile beam oppositethat which is located facing the network 6.

In this case, the exit microguide 4 does not go beyond this beam 26(when moving away from the network 6).

In one mode of embodiment not shown, the micromonochromator according tothe invention includes the entry microguide 2 of which one extremity islocated on the mobile beam 20 but does not include any exit microguide.

The microguide(s) are then replaced by one or several photodetectors.

Instead of using a step grading as means of diffraction, a microguidenetwork or PHASAR can be used as illustrated schematically in FIG. 6.

The micromonochromator according to the invention which is schematicallyrepresented in an overhead view in FIG. 6 includes such a network ofmicroguides 38.

On one side of it there is an entry microguide 2 of which one extremityis formed on a mobile beam 20 in a free space 22 provided on thesubstrate.

The means of movement control for this beam are not shown in FIG. 6.

The exit microguides 4 of the micromonochromator are located on theother side of the microguide network 38.

FIGS. 1, 2 and 6 are given as examples with 1 entry and N exits.

There could of course be N entries and 1 exit (in the case of amultiplexer) or N entries and M exits (the mobile means being preferablylocated on the side of the entries if N<M or the exit side if M<N).

As an example, the multiplexer could correspond to FIG. 2 with themicroguide network 4 at the entry and the microguide 2 at the exit,reference 23 corresponding to the various wavelength sources.

FIG. 7 schematically illustrates a micromonochromator according to theinvention which includes several mobile beams 20 at the entry forexample, each beam being equipped with a microguide 2. Amicromonochromator could also be made according to the invention withseveral mobile beams at the exit (each equipped with a microguide) oreven several mobile beams at the entry and exit.

These mobile entry and exit beams can be independent of each other andthus controlled independently of each other (as in FIG. 7) or, on thecontrary, they can be rigidly attached to each other and controlledsimultaneously. There could even be several mobile beams at the entryand exit, all of these beams being controlled simultaneously (this isillustrated in FIG. 4 in the case of an entry and exit beam).

In addition, any mobile entry beam can be equipped with a source oflight placed directly on this beam. Any mobile exit beam can likewise beequipped with a photodetector (as shown schematically in FIG. 3 in thecase of a single exit beam).

It should be noted that the use of at least one mobile beam which cansweep that entry and/or the exit continuously is of great value for theinvention. Particularly in the case of a multiplexer, such an entry beamallows for multiplexing of any wavelength (as can be seen from FIG. 7),whereas if the mobile beam cannot be continuously varied, onlywavelengths determined in advance could be multiplexed. Likewise in thecase of demultiplexing, such an exit beam allows for demultiplexing ofany wavelength.

What is claimed is:
 1. Micromonochromator formed in an integratedsubstrate and including: at least one entry means for light guidance; atleast one exit means for light guidance; means for diffraction, thediffraction means being between the at least one entry means and the atleast one exit means and along the light way therebetween, and beingintegrated in the substrate; and mobile means for light guidance, themobile means being between the at least one entry means and the at leastone exit means and along the light way therebetween, and including atleast one mobile beam integrated in the substrate and equipped with atleast one light guide, the mobile beam being able to sweep thediffraction means in a continuous manner; whereby one desired wavelengthcarried by an optical wave that enters the at least one entry means isrecovered in the at least one exit means when the mobile beam isadjusted to a selected position with respect to the diffraction means.2. Micromonochromator according to claim 1, in which the mobile means oflight guidance includes: a first mobile means of light guidanceassociated with the entry of the micromonochromator, and a second mobilemeans of light guidance associated with the exit of themicromonochromator, the mobile beam being one of first and second mobilebeams, the first and second mobile means of light guidance including,respectively, at least the first mobile beam integrated in the substrateand equipped with at least a first light guide, the first mobile beambeing able to sweep the entry in a continuous manner, and at least thesecond mobile beam integrated in the substrate and equipped with atleast a second light guide, the second mobile beam being able to sweepthe diffraction means in a continuous manner.
 3. Micromonochromatoraccording to claim 2, in which the first and second mobile beams areindependent of each other.
 4. Micromonochromator according to claim 2,in which the first and second mobile beams are rigidly attached to eachother.
 5. Micromonochromator according to claim 1, in which thediffraction means includes a multiple-facet mirror. 6.Micromonochromator according to claim 1, in which the diffraction meansincludes a network of light microguides.
 7. Micromonochromatormanufacturing process according to claim 1, characterised in that thediffraction means and the mobile means are integrated in the substrate.8. Micromonochromator formed in an integrated substrate and including:at least one entry means for light guidance; a plurality of exit meansfor light guidance; means for diffraction, the diffraction means beingbetween the at least one entry means and the plurality of exit means andalong the light way therebetween, and being integrated in the substrate;and mobile means for light guidance, the mobile means being between theat least one entry means and the plurality of exit means and along thelight way therebetween, and including at least one mobile beamintegrated in the substrate and equipped with at least one light guide,the mobile beam being able to sweep the diffraction means in acontinuous manner, whereby one desired wavelength carried by an opticalwave that enters the at least one entry means is recovered in a selectedexit means of the said plurality of exit means when the mobile beam isadjusted to a selected position with respect to the diffraction means.9. Micromonochromator according to claim 8, in which the mobile means oflight guidance includes: a first mobile means of light guidanceassociated with the entry of the micromonochromator, and a second mobilemeans of light guidance associated with the exit of themicromonochromator, the mobile beam being one of first and second mobilebeams, the first and second mobile means of light guidance including,respectively, at least the first mobile beam integrated in the substrateand equipped with at least a first light guide, the first mobile beambeing able to sweep the entry in a continuous manner, and at least thesecond mobile beam integrated in the substrate and equipped with atleast a second light guide, the second mobile beam being able to sweepthe diffraction means in a continuous manner.
 10. Micromonochromatoraccording to claim 9, in which the first and second mobile beams areindependent of each other.
 11. Micromonochromator according to claim 9,in which the first and second mobile beams are rigidly attached to eachother.
 12. Micromonochromator according to claim 8, in which thediffraction means includes a multiple-facet mirror. 13.Micromonochromator according to claim 8, in which the diffraction meansincludes a network of light microguides.
 14. Micromonochromatormanufacturing process according to claim 8, characterised in that thediffraction means and the mobile means are integrated in the substrate.